Generally, composite materials are prepared by imbedding a reinforcing material within a matrix material. A common example of a composite material is fiberglass. Fiberglass is glass fibers, which are the reinforcing material, embedded in a cured polymeric resin, which constitutes the matrix material.
The utility of any composite is typically related to its high strength or stiffness to weight or volume ratio and, sometimes, to its fatigue or corrosion resistance. Such beneficial properties of composites are typically a result of load sharing between the matrix materials and reinforcing materials. In most instances, these beneficial properties exceed those of the materials supplanted by the use of the composites.
Two general classes of composite materials are metallic composites and polymeric composites. Metallic composite utilize metal as the matrix material. Metallic composite are sometimes referred to as metal matrix composites. Suitable metals for use as the matrix may be alloys or pure metals. Metallic composites may utilize fibrous or particulate reinforcements. Fibrous reinforcements can be continuous or discontinuous with random or specific orientations. Such fibers may be comprised, for example, of ceramic materials such as aluminum oxide, silicon carbide, and carbon. Particulate reinforcements may be comprised of, for example, metals, ceramic materials such as metal oxides, carbides, nitrides, and borides, and intermetallic compounds.
As a result of their typically high strength to weight, or volume, ratios, metallic composites, particularly those comprised of low density metals such as aluminum and magnesium, have potential utility in numerous applications. However, metallic composites have been used in only a very limited number of applications and can typically very costly to manufacture.
Polymeric matrix composites utilize any of a number of different polymeric compounds as the matrix material. Such polymeric compounds can include thermoplastic and thermosetting plastics, resins, epoxies, and the like. Matrix materials can include fibers or particulates. Most commonly, high strength fibers, such as those of glass, aramid, or graphite, are used as the reinforcement material. When used in a composite, such fibers may be continuous, discontinuous, or utilized as a mat or cloth, and have a specific or non-specific orientation. A number of materials have been used as particulate reinforcements in polymeric composites. For example, glass, sand, and calcium carbonate particulates are commonly used as the reinforcement in polymeric particulate composites.
Polymeric composite materials have been found to have a high degree of utility when used as parts of structures, components, sub-assemblies, and the like, of assemblages such as aircraft, missiles, boats, medical equipment, and sporting goods. A polymeric composite commonly used in such applications is fiberglass. Other composites having particularly high degrees of utility in such applications are those that are prepared from carbon fibers combined with a polymeric matrix material such as thermosetting and/or thermoplastic polymeric resins. Such composites are referred to as carbon fiber composites, or more commonly, carbon composites. Carbon composites have been used, for example, in such diverse applications as aircraft flight surfaces, missile bodies, orthopedic supports, and golf club shafts.
Sometimes, it is determined that a polymeric composite part as originally envisioned or designed will not provide desired levels of strength and/or rigidity. In such instances, additional structural support may then be incorporated into the part. Such additional structural support may be provided by increasing the thickness of the polymeric composite part or by adding bracing, such as metal bracing or polymeric composite bracing, to the exterior of the part. Additionally, such bracing may be provided by embedding a metal structure or polymeric composite reinforcement structure into the polymeric composite part such that the reinforcement is essentially enclosed within the material of the polymeric composite part.
Such methods for providing additional structural support can substantially increase the strength and/or rigidity of the polymeric composite part. Unfortunately, such methods also can lead to a significant increase in the volume and/or mass of the resultant composite part. Increasing the thickness of the polymeric composite increases the mass and volume of the part. Flexural and overall strength of a composite part may be improved by the use of polymeric composite bracing, but such bracing can also result in significant increases in part volume and mass.
Generally, the use of metals as reinforcement structures, especially embedded reinforcement structures, can result in a significant increase in the composite part strength with a minimal increase of the composite part volume. The form of the metals used can include, but is not limited to, rods of square, rectangular, or circular cross-section, tubes, and flats. Unfortunately, such benefits are usually accompanied by a significant increase in the mass of the resultant composite part. For some demanding applications, such as aerospace applications, a significant increase in the volume and/or mass of the resultant composite part can limit, or even eliminate, the utility of the part.
Therefore, increasing the strength and/or rigidity of polymeric composite parts, without incurring a significant weight and/or volume penalty and that utilizes available constituents, would have utility in many applications.